1. Field of the Invention
This invention relates to chair irons. In one embodiment, the invention relates to a low profile chair iron useful for controlling tilting between a seat and a supporting base therefor. In another of its aspects, the invention relates to a low profile chair iron useful for controlling tilting of the chair backrest with respect to the chair seat and/or supporting base therefor.
2. State of the Prior Art
In the office equipment field, chairs having tilt mechanisms are common. Typically, the chairs are supported on wheeled pedestal bases. The mechanism, which couples the base to the seat is known as a "chair iron." In tilting chairs, the chair iron typically includes a threaded spindle rod extending upwardly from a wheeled multiple foot base, a collar threaded on the spindle for adjusting the vertical position of the chair, a first bracket rigidly secured to the underside of the chair and a second bracket pivotably mounted to the first bracket and rigidly secured to the spindle. In the case of a secretarial or posture chair, the one bracket is secured to a backrest and the second bracket is secured to the spindle or seat. The brackets are biased with respect to one another about the pivot axis and tilting takes place against the bias.
Many different techniques have been employed for biasing the brackets with respect to one another. Cylindrical coil springs, for example, are common and are illustrated in the U.S. Pat. to Hamilton, No. 2,729,273 (issued Jan. 3, 1956). The U.S. patent to Engstrom, No. 3,656,805 (issued Apr. 18, 1972), discloses a similar type of chair iron which uses a frustroconically shaped spring.
In recent years, it has become more important to provide a low profile to the chair iron to give a more sleek appearance to the chair assembly. The chair irons employing the cylindrical coil spring types of biasing means are generally more bulky and crude in appearance with the coil spring being visible.
Accordingly, a number of different types of chair irons have been developed to achieve a low, sleek profile. Torsion bars have proved to be a popular type of biasing means. An example of a torsion bar chair iron is illustrated in U.S. Pat. No. 2,935,119 to Lie issued May 3, 1960. Although it is low in height, the torsion bar chair iron is quite wide and has a bar extending out of each end thereof. This wide structure is becoming less desirable in curved bottom plastic shell chairs.
Other types of lower profile chair irons include rubber bushed or coil springs wrapped around the pivot bolt between the tilting and stationary brackets. Examples of these types of chair irons are illustrated in U.S. Pat. No. 3,881,772, issued May 6, 1975.
Flat leaf spring chair irons have also been used to provide the biasing between the tilting and stationary brackets. These types of chair irons are illustrated in U.S. Pats. Nos. 391,822 (issued Oct. 30, 1888), 2,818,911 (issued Jan. 7, 1958), 3,693,925 (issued Sept. 26, 1972).
Other types of chair irons have taken completely different forms. A cylindrical coil spring wrapped around a spindle and positioned within a telescoping housing is used to bias a tilting bracket with respect to the fixed bracket in U.S. Pat. No. 3,720,396, issued Mar. 13, 1973. The use of spring compression washers to bias the tilting bracket with respect to the fixed bracket is illustrated in the U.S. Pat. No. 3,814,369, issued June 4, 1974. The use of C-shaped flat springs as biasing means between the tilting and fixed brackets is disclosed in U.S. Pat. No. 3,284,133, issued Nov. 8, 1966. The use of a C-shaped leaf spring construction for the tilt bias is illustrated in U.S. Pat. No. 3,740,792, issued June 26, 1973.
Each of these chair irons disclosed is relatively expensive to produce or has some degree of difficulty in adjusting the tension within the biasing means. Further these chair irons, other than the torsion bar type, cannot practically achieve an acceptable low profile for more modern chairs.